No, no - all I was pointing out was that "volatile" was of no use to me - and I certainly don't mean to imply that you claimed it *would* be of any use to me. In the PDL source I've had to use #pragma optimize("", off) to get the desired behaviour. The conditional test that's causing all the problems in the autogenerated bad.xs is:

if((a_datap)[0] /* ACCESS() */  == (PDL_Float) __privtrans->value )
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where (a_datap)[0] is a float and __privtrans->value is a double. With all but the pre-VC8.0 compilers, that behaves as desired and expected. My initial attempt at a fix (from the replies received here) for the pre-VC8.0 compilers was to replace that with:

PDL_Float dummy = (PDL_Float) __privtrans->value;
if ( (a_datap)[0] /* ACCESS() */  == dummy )
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All of the playing around that I've done with C scripts suggests that that should have worked ... but it didn't. I still got FALSE evaluations when I wanted and expected the evaluation to be TRUE. If I make 'dummy' volatile, that doesn't make any difference. One way I can get that modified code to behave correctly is to turn off optimization using #pragma. That is, for pre-VC8.0 MS compilers, the code (which behaves correctly) is:

#pragma optimize("", off)
PDL_Float dummy = (PDL_Float) __privtrans->value;
if ( (a_datap)[0] /* ACCESS() */  == dummy )
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A patch that provides a better fix will always be most welcome. (It may be relevant that optimization is off for some of the other code as well - not just for the creation of the dummy variable and the testing of the == condition. The optimization cannot be turned on/off inside subroutines.)

Btw, in case there's a need to mention it, the PDL_Float type is typedef'd as follows:

typedef float              PDL_Float;
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Cheers,
Rob